High speed thermal printer



Nov. 5, 1968 J. o. MERRYMAN 3,4099% HIGH SPEED THERMAL PRINTER Filed May27, 1966 4 Sheets-Sheet 1 INTERFACE DATA SOURCE NV ENTO R JERRY D.MERRYMAN ORNEY 1968 J. D. MERRYMAN HIGH SPEED THERMAL PRINTER 4Sheets-Sheet 2 Filed May 27, 1966 m Om m M MR H mm wm M Wm m vw A W E XJ xUO G ommam IO I WE mm om Nov. 5, 1968 J. D. MERRYMAN HIGH SPEEDTHERMAL PRINTER 4 Sheets-Sheet 5 Filed May 27. 1966 Vcc INVENTOR F G- 6JERRY 0. MERRYMAN 1968 J. D. MERRYMAN HIGH SPEED THERMAL PRINTER 4Sheets-Sheet 4 Filed May 27. 1966 L mwkwRv Em Cm 1 m6 15mg E56 Kim .5208

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V51"; E on United States Patent "ice ,HIGH SPEED THERMAL PRINTER l-JerryD. Merryman, Dallas, Tex.,assignor to Texas Instruments Incorporated,Dallas, Tex., a corpoe ration of Delaware May 27, 1966, Ser. No. 553,420

Filed 6 Claims. (Cl. 34676) 3,409,902 Patented Nov. 5, 1968 of theperiphery of the drum. Serial data is fed to the data converter meansthrough slip rings and appropriate steering logic also carried by thedrum' during the period when the paper is not in contact with therespective print heads to which the information pertains. The hot spotsare then turned on in accordance with the data during the remainder ofthe revolution of the drum, and while in contact with the paper, eachhot spot marks the heat sensitive paper to reproduce the data. A singlechannel may be used for input information, or a plurality of channelsfor the input information may be used in parallel to reduce the rate atwhich the serial information is supmemorymeans carried by the. rotatingdrum. The mem- I ory. means. receives serial data and converts theserial data to parallel data at a plurality of outputs associatedwithindividual heating elements to produce preselected patterns ofheated elements.

This invention relates generally to thermal printing, and moreparticularly relates to a high speed thermal print head suitable for useas a readout system for digital data storage and processing systems, andthe like.

There are a great many applications forhigh speed printing devices. Forexample, the speed of many computers and data handling systems islimited by the rate at which data can be read out in printed form.Similarly,

the rate at which written and pictorial information can t An importantobject of this invention is to provide a very high speed system forprinting alphanumeric, pictorial, or other data from digital logic data.

' Another object is to provide an alphanumeric readout for a high speeddigital computer or the like.

Another important object of the invention is to provide such a highspeed printer having a cost compatible with the service rendered.

A further object is to provide such a system which is more compact thanpresently existing slower printers,

and which has a minimum number of moving parts and a long and troublefree life.

' Still another object is to provide a high speed printing devicesuitable for use as a readout device for large, high speed memories,as'a high speedfacsimile printer, or as a real time pictorial recorderfor a television signal or the like.

In accordance with the present invention, these and other objects areaccomplished by a rotating drum which carries a plurality of thermalprint heads. The thermal print heads extend longitudinally of the drumand are spaced around the periphery of the drum. Each print headincludes a matrix of individually controlled hot spots arranged toproduce alphanumeric, pictorial-or other information when selectivelyenergized. Each hot spot is controlled by information stored in aserial-to-parallel data converter such as a shift register carried bythe rotating drum. A heat sensitive paper is passed around the drum asit rotates, but is in contact only with a portion plied to the drumthrough any one channel.

Thenovel features believed characteristic of this invention are setforth in the appeded claims. The invention" itself, however, as well asother objects and advantages thereof, may best be understood byreference to the following detailed description of illustrativeembodiments, when read in conjunction with the accompanying drawings,wherein:

FIGURE 1 is a schematic side view of a thermal printing deviceconstructed in accordance with the present invention;

FIGURE 2 is a simplified sectional view taken generally on lines 2-2 ofFIGURE 1;

FIGURE 3 is a schematic logic and circuit diagram of the thermalprinting device of FIGURE 1;

FIGURE 4 is a simplified perspective view of a typical thermal printhead used in the device of FIGURE 1;

FIGURES is a simplified sectional view of the thermal print head ofFIGURE 4;

FIGURE 6 is a schematic circuit diagram of a heater circuit of thethermal print head of FIGURE 4; and

FIGURE 7 is a schematic logic and circuit diagram of an alternativeembodiment of a thermal printing device constructed in accordance withthe present invention.

Referring now to the drawings, a thermal printing device constructed inaccordance with this invention is indicated generally by the referencenumeral 10 in the schematic illustration of FIGURE 1. The printingdevice 10 is comprised of a'cylindrical drum 12 mounted on a rotatingshaft 14. The shaft and drum is driven by some suitable meansrepresented by the motor 16 at a preselected speed. As can be seen inFIGURE 2, a length of heatsensitive paper 18 passes around the cylinder12 as the cylinder 12 rotates, and is in contact with the cylinder overappriximately 180 of its circumference. The paper 18,may be either acontinuous strip, or a series of sheets, and a suitable conventionalmeans is provided to handle the paper.

The particular embodiment of the print head presently to be described isadapted to print lines of alphanumeric characters. This is accomplishedby fifty thermal print heads P -P which extend longitudinally of thedrum 12 and are equally spaced around the periphery of the drum. Each of'the fifty print heads P -P is comprised of one hundred twentyalphanumeric character matrices c c (see FIGURE 3), and each of thecharacter matrices is comprised of twenty-five individually controlledhot spots 20. Thus, as illustrated in the schematic logic diagram ofFIGURE 3, character matrices C C of print P are designated as 'P C P Cthe character matrices of print head P are designated as P c, P c, andfinally the character matrices of the print head P are designated as P CP C Thus, it will be noted that eachof the print heads. P P has threethousand individually -controllable hot spots 20.

Each of the thermal print heads P P may be fabricated, for example,using the method described in copending US. application Ser. No.492,174, entitled Thermal Print head, filed on Oct. 1, 1965 by StephenP.

Emmons et al.. anddassignedto,theassignee of the present I invention.More particularly, each of the hot spots 20 may be comprised of a bodyof semiconductor material 54 (see FIGURE 5)- covered by a layer ofsilicon carbide 57. The silicon carbide surface layer 57 is in directcontact with the paper 18 and provides a highly wear re-, sistantsurface. Each of the hot spots 20 isheated by a heater circuit,indicated generally by the reference numeral 56 in FIGURE 6, thecomponents of Which are formed by diffusion or other conventional,techniques within the semiconductor bodies 54. The heater circuit 56 iscomprised of transistors 58'. and 60: and collector resistors 62 and 64,connected in the conventional man ner illutrated. Thebase 66 oftransistor 58 is the control input of the heater circuit. When a logicFOlevel, i.e., 0.0 volt, is applied to terminal 66, the heater circuitisturned off. When a positive voltage representatiyeof a logic 1 level isapplied to the control terminal 66, transistors 58 and 60 conduct, andthe current through the transistors and through the collector resistorsheats the entire semiconductor body 54 and theoverlying silicon carbidelayer 57. The leads interconnecting the transistors and resistors of theheater circuit 56 and the input leads and voltage supplies for thevarious heater circuits of the matrix may be formed as first and secondlayer interconnections 68 and 72 formed on oxide layers 70 and 74. Thirdor fourth level interconnections may, of course, be used if necessary.The structure thus far described is mounted on a ceramic substrate 76 bya suitable bonding material 78, such. as epoxy. The leads to thevariousheater elements 56 may then extend down the edge of the ceramicsubstrate 76, as represented schematically by the structure designatedwith the reference character 80* in FIG- URE 4. Each adjacent pair "ofcharacter matrices, for example matrices P C and P may be separatedby araised bar 82 formed by semiconductor body 84 and covered by the siliconcarbide layer 57.

The print head illustrated in FIGURES 4, and 6 may be fabricated byfirst etching out grooves in the surface of a semiconductor body to formmesas corresponding to the semiconductor bodies 54 and 84. This maybeaccomplished using conventional photolithographic etching techniques,Then the silicon carbide layer 57 is deposited over the surface of themesas and the grooves. This may be accomplished using, for example, amixture of tolulene (CH and silicon tetrachloride (SiCl vapors withhydrogen gas as the carrier. These gases, in atypical ratio of aboutO.87mole percent silicon carbide, 0.18 mole percent tolulene, and theremaining mole percentage hydrogen, are passed over the substrate whichis located in a suitable heated furnace and maintained at a temperatureof about 1080 C. Next, a layer of polycrystalline or amorphous siliconis deposited over the surface of the silicon carbide layer by thehydrogen reduction of silicon tetrachloride, for example. This layer isnot illustrated in the drawings because it is used merely to lendstructural rigidity during processing and is subsequently removed. Thesurface of the semiconductor starting material opposite from the bodies54 is then removed by lapping and polishing down to the silicon carbidelayer 57 previously formed in the grooves. This leaves single crystalsemiconductor bodies 54 as islands at the surface of the amorphoussilicon body, the silicon islands being isolated from the amorphoussilicon body by the silicon carbide layer 57. The silicon carbide layer57 serves to limit the depth of the lapping and polishing process andassures that the thickness of the semiconductor bodies 54 will beuniform, thus insuring uniform heating and cooling rates for all of thehot spots.

The transistors and. resistors can then be fabricated in the exposedsurface of the semiconductor bodies 54 using any standard fabricationtechnique, and the various lead patterns formed in one or more layers onthe surface of the substrate. This structure is then inverted andmounted on the ceramic substrate 76 using-the bonding layer 78,-afterwhich the amorphous layer of silicon'is removed from the silicon carbidelayer by a suitable etchant, such as a mixture '-of hydrofluoric acid,nitric acid and acetic acid. During this step of the process, thesilicon carbide layer 57 acts as an etch barrier to protect theunderlying silicon bodies 2'4,"afld permit the amorphous silicon tobeetched from the grdo've sbe't ween the various hot spots. W

Referring. once again to. FIGURE 3, fifty shift registers DSR -DSR Q,are provided fonthe. fifty print heads P P respectively. In order tohave maximum flexibility, each shift register has a three thousand-bitstorage capacity, and each bit iscormected to control-one of. the hotspots 20. The shift registers are serial-to-parallel data converters inthat three thousandb'its of'bina'ry data may be seriallyfed into-eachregisterjthen'the. three thousand bits of'data are stored and'convertedto three thousand parallel outputs'to control the corresponding hotspots. When-onlyi alphanumeric information is to belprinted by thedevice 10, only thirty of forty characters will need to be printed byeach charactermatrix. The number of bits in theshift registers DSR foreach character can then be reduced from twentyfive to about six ifanappropriate decoding-circuit is in= cluded to convert the six bitbinary code was to control the hot spots of the character matrix in sucha manner as to produce the limited number of characters.

The data shift registers DSR DSR are preferably 10- cated adjacent tothe print heads P -P substantially'as illustrated in FIGURE 2. The shiftregisters DSR DSR may be fabricated as integrated circuits occupyingabout the same volume of space as the print heads P P However, it willbe appreciated that as much space as is required within the interior ofthe drum may be used for the shift registers, ring counter and steeringgates presently to be described.

Fifty data gates DG DG and fifty clock gates CG;- CG are sequentiallyenabled by the outputs from the fifty bits b 42 of a ring counter RC.The ring counter RC is clocked by a low speed clock pulse train appliedthrough slip ring 22 on the shaft 14, the slip ring input beingdesignated by the same reference character in both FIGURES 1 and 3. Thefrequency of the low speed clock pulse train is equal to the number ofdata shift registers DSR times the speed of rotation of the drum 12.Thus, if the drumis rotated'at fifty revolutions per second, the lowspeed clock would have a frequency of 2500 pulses per second. The outputfrom the last bit b of the ring counter-may be fed out through slip ring24 for synchronization purposes. The

outputs from bits b b of the ring counter RC sequentially enable inputdata gates DG DG respectively, and high speed clock gates CG CGrespectively.

A high speed clock signal is applied to the rotating drum and then to aninput of each of the clock gates CG CG through slip ring 26. Thefrequency of the high speed-clock is at least equal to the product ofthe total number of storage bits in the fiftydata shift registers DSRDSR and the speed of rotation of the drum 12, plus a slight margin tofacilitate operation of the steering logic, as will hereafter bedescribed. Input data is applied to the inputs of data gates DG DGthrough slip ring 28. .The input data is in serial binary form, and issynchronized with the clock pulses applied through slip ring 26.Thus,the data signal would be at either a logic 0 or a logic 1 levelduring each of three thousand clock pulses, depending upon the-binaryvalue of the bit. Each successive bit of data is introduced to one endof the shift reg'ister,'then shifted through the remaining'bits of theregister. After the three thousandth clock pulse, each of the threethousand bits of-the shift register has the appropriate output, andthese outputs are fed in parallel to control the three thousand hotspots-until new data is fed into the shift register.

Electrical power for all of the circuits is applied through slip rings30 and 32, it being understood that the two slip rings are merelyexemplary and that as many slip rings as required can be provided tosupply voltage supplies of differ'en't levels.

A pair of timing disks 34 and 36 are mounted on the shaft 14 in order tosense the position and speed of the drum 12 as represented in FIGURE 1.Fifty permanent magnets may be spaced around the periphery of'the disk34 to induce fifty pulses in the pickup head 38 during each revolutionof the drum 12, the magnets preferably being positioned to correspond tothe positionof'the print heads P -P5 respectively. The pulse trainproduced by disk 34 and pickup head 38 may be used to either synchronizeor derive the low speed clock pulses used to operate the ring counterRC. A single'r'nagnet may be provided on disk 36 for inducing a singlepulse in pickup head 40 during each revolution'of the drum '12. Thispulse is used as a reference to determine the position of the drum 12,and from this pulse and the pulses from' output 24, the operation of thering counter RC is synchronized with the rotation of the drum. Thus, themagnet and pickup head may be located to produce a pulse' when printhead P is in the position illustrated in FIGURE 2, for example,indicating that bit b of the ring counter should have a logic 1" outputto enable the gates DG and C6 as will--now be described.

The printing device is made compatible with asource of data 44 by aninterface 42. The data source may be. any

desired high speed memory, computer, or-other data processing system.The interface 42 takes the data from the source 44 and puts it indigital form suitable for operating the printing device 10, andsynchronizes the supply ofdata with the operation of the printingdevice. The interface may vary widely in design and construction,depending upon the nature of the data provided by-the source, butperforms the primary function of supplying thebinary data to be recordedby each of the print heads to the appropriate print head as the printhead passes-through the data input are (see FIGURE 2). To this end, the

interface may control the rotation of the drum as represented by line 46extending to motor 16. Thus, the interface provides an input data signalin theform of three thousand bits of serial data synchronized with threethousand clock pulses within thedesired interval, and insures that theoperationof the ring counter is synchronous with the rotation of thedrum so that the steering gates DG and C0,, are enabled at theappropriate time. a

In the operation of the device 10, the drum 12 is rotated at somedesired constant speed, suchas fiftyrevolutions per second. The ringcounter RC would then operate at a rate of twenty-five hundred countsper second; The count ofthe ring counter RC is synchronized with theposition of the drum 12 so that the output from bit b enables gates DGand 'CG during the period that print head P passes through the input are50 equal to no more than one-fiftieth ofone revolution. Thenasprintheads P P etc. successively passthrough the are 50, gates DG and C6 DG3and C6 etc. are successively enabled by the output from bits b b etc. ofthe ring counter RC.

Coincident with the enabling of gates DG and CG three thousand bits ofserial binarydata are introduced through slip rings 26 and 28 inthe'form of-a data signal level synchronized with three thousand clockpulses. The serial data is't-hen stored indata shift register DSR andconverted into parallel digital data to simultaneously control the threethousand hot spots 20 of print. head P and form the desired characterswithin the one hundred twenty character matrices, P C P C As the drum 12continues to rotate, registers DSR -DSR ,v are sequentially loaded asthey pass through the arc 50. During Thus, it will be noted that byusing fifty print heads and a drum 'speedof fifty revolutions persecond, twentyfive hundredlines per second are printed with each linecontaining one hundred twenty characters. Of course, this can beincreased or decreased as 'desiredby variationsin the 'numberof printheads and in the speed of rotation of the drum. The particular number ofprint heads and the particular speed of rotation was selected merely asexemplary, and the components herein described for accomplishing' thisrate are presently within the state'of the art. p

The rate at which the input data is supplied to the various data shiftregisters DSR DSR is rather high, being 7.5 million bits per second inthe particular embodiment described. Thus, the shift register DSR mustoperate at a rather high frequency. Ari alternative embodiment of theinvention in which the frequency of the input data is reduced isindicated generally by the reference numeral in FIGURE 7. The printingdevice 100 is very similar to the printing device 10 and correspondingparts are therefore designated bycorresponding reference numerals. Theprinting device 100 differs from the printing device 10 principally inthat five shift registers, each having a six hundred bit capacity, areprovided for each of the fifty print heads, rather than a single shiftregister having a three thousand bit capacity. Thus, data shiftregisters DSR ,,--DSR control the individual hot spots of print head Pdata shift registers DSR DSR control the individual hot spots of printhead P etc. The shift registers DSR ,.,DSR are simultaneously loadedwith data through slip rings 102-106 and data gates DG DG when the gatesare enabled by an output from bit b; of the ring counter RC. Similarly,shift registers DSR ,,DS R are simultaneously loaded 'through gates DGgDG when bit b of the ring counter RC has a logic 1 output. Clock gate(36 gates the clock pulse train to all five of the shift registers DSR'-DSR and clock gate CG gates the clock pulse train to-registers DSR-DSR etc.

The operation of the printing device 100 is identical to the operationof the device 10 except that the serial binary input data toeach of thefive shift registers for each of the print heads is loadedsimultaneously, i.e., in parallel, from the five separate slip rings andsteering gates so that the rate at which the data is put into theindividual storage means, and thus the rate at which the shift registersmust operate, is reduced by one-fifth. It will readily be evident thatthe'number of shift registers for each print head may be increased ordecreased to decrease or increase, respectively, the rate at which datais serially put into the individual shift registers. Thus, in theprinting device 100, the data is provided at a rate of 1.5 million hitsper second as opposed to 7.5; million bits per second in the printingdevice 10.

Although the embodiments of the invention herein described have beenspecifically directed toward printing lines having one hundred twentyalphanumeric characters, it is to be understood that substantially anytype of data may be printed in accordance with the broader aspects ofthe invention. or example, the entire surface of the drum may form asingle matrix of hot spots. The matrix may be divided in a convenientmanner into two or more sections and one or more shift registersprovided for each section. The shift registers for the matrix sectionsmay then be sequentially loaded during the portion of the revolutionthat the matrix section is not contacting the paper. In the event aplurality of shift registers are used to control each matrix section,the shift registers can be loaded in parallel.

From the above detailed description of the invention, it will be notedthat an extremely high speed printer has been described. The printingdevice is compatible with high speed data processing systems and can beused as the data readout for such systems. The printing device can beused as a high speed facsimile read-out device. By

way of examplejth e device hereindescribed has sufficientspeedcapability to record, in real time, the successive fra'mespfconventional television transmission.

What is claimed is: i I I I i 1; A thermal printing device forselectively applying heat to a thermally sensitive membercomprisingz'drum means having a matrix of controllable heating elements formed onthe surface thereof for selec- I tively heating predetermined areas onthe thermally sensitive member when the predetermined areas are adjacentto said heating elements, means. forrotatingsaid drum means, memorymeans carried by said ,druin means for re- -ceiving serial data andstoring andnconverting the serial datato paralleldata at a plurality ofparallel Outputs from said memory means, 1

,the parallel outputs beingconnected to activate associated heatingelements in accordance with the data at the respective outputs toproduce preselected patterns of heated elements, ,means for supplyingthe serial data to the memory means during a portion of each.revolutionof the drum means as said associated heating elements are being rotatedtoward a position adjacent the predetermined areas on the thermallysensitive member,

whereby the heating elements are activated in the preselected patternduring the portion of the revolution of the drum means when the heatingelements are adjacent the predetermined areas of the thermally sensitivemember. 2. In a thermal printing device, the combination of: drum meanshaving a matrix of controllable heating elements formed onthe surfacethereof for selectively heating predetermined spots on a heat sensitivesheet disposed adjacent thereto, memory means for receiving serial dataand storing and converting the serial data to parallel data at aplurality of parallel outputs, the parallel outputs being connected toactivate the heating elements in accordance with the data at therespective outputs, means for rotating the drum means, and means forsupplying serial data to the memory means during a portion of eachrevolution of the drum means whereby the heating elements will beactivated in a pattern determined by the data during the remainingportion of the revolution of the drum means such that the pattern may beimpressed upon a heat sensitive sheet moving with the drum meansadjacent the heating elements during said remaining portion of therevolution, said means for supplying the serial data comprising meansfor transferring a data signal from a fixed circuit to a circuitrotating with the drum means, gating circuit means carried by the drummeans for selectively applying the data signal to the memory means whenthe gating circuit means is enabled, and

synchronizing circuit means carried by the drum 7 I means and responsiveto the position of the drum means for enabling the gating circuit meanswhen said matrix is traversing said portion of each revolution of thedrum means. 3. In a thermal printing device, the combination of: drummeans having a plurality of matrices disposed at circumferentiallyspaced points around the periphery thereof, each matrix comprising aplurality of controllable heating elements arranged to produce selectedpatterns on a heat sensitive sheet disposed adjacent to the matrix,shift register means for each matrix for receiving serial data andstoring the data as parallel data appearing at a plurality of paralleloutputs from the shift register means, e

circuit means connecting the parallel outputs of the shiftregist'enme'ans to'the controllable heating elel ments of therespectivematrices for controlling; the heating elements 'of the matrices in "a'manner detera a set of shift register. means for 'minedrby the data atthe parallel outputs to produce I I: selected patterns ofheatedelementsin the respective Imatrice.-;, .v 1.? r ,.:-Y.-

means for; rotating :the drum. means, and I II means for supplyingserial data to the shift register means as the drum means rotates, theserial data being supplied to'feach of the shiftre'gister means i as thematrix controlled by the shift register means I travels through apredetermined portion of a revolution 'fi he d me n i v ,whereby theheating elements will be activated in patterns determined by the datastored in the respective shift register means, and will ,rejrnainfactivated during th e remaining portion ofthe revolutionof the drummeans to impress a pattern upon a heat serrsitive sheet'rotating withthefdrum means adjacent the heating elements during said remainingportion ,of the revolution of the dru'm means, j 4. T l 1ecombinationdefined in claim.3wherein th e means for supplying serialdata to, the shift register means supplies serial data to a plurality ofthe shift register means at the same time.

5. The combination defined in claim 3 .wherein the means for supplyingserial data to the shift register means comprises: r I v I a data gatecarried by the drum means for each shift register. means, each data gatebeing connected to supply a data signal. to the respective shiftregister means when enabled, i .first circuit means carried by the drummeans for-receiving. a data signal from a source without the drummeansand applying the data signal to each of the data gates,

'' a clock gate carried by the drum means for each shift register means,each clock gate being connected to supply a clock pulse train to therespective shift register means when enabled,

, second circuit means carried by the drum means for a receiving a clockpulse train synchronized with the data signal from a sourcewithout thedrum means and applying the clock pulse train to each of the clockgates, and I synchronization circuit means. carried by the drum meansand connected to selectively enable each of the gate means, saidsynchronization circuit means being adapted to receive a synchronizationsignal related to the rotational position of the drum means and, inresponse to the synchronization signal, enable the gate means related tothe respective matrices as the respective matrices pass through said.predetermined portionof the revolution of. the drum means. r v r 6. Ina thermal printing device, the combination of:

a drum means having a plurality of matrices disposed atcircumferentially spaced points around the periphery thereof, eachmatrixcomprising a plurality of controllable heating" elements arranged toproduce selected patterns on a heat sensitive sheet disposed adjacent tothe matrix, I a

each matrix, each a shift register means being adapted to receive serialdata and store the. data as parallel data appearing at a plurality ofparallel outputs from the shift register means, t =-circuit meansconnecting the parallel outputs of the plurality of.shift register meansfor. each matrix to the controllable heating elements of the respectivematrix for controlling the heating elements in a a manner determined bythe'data at the parallel out- ,7 puts of the .shift register means toproduce selected :rpatterns of activated, heating elements;intherespective matrix,

means for rotating the drum means, a set of data gates carried by thedrum means for each set of shift register means, each data gate beingconnected to supply a data signal to one of the shift register means ofthe set when enabled,

a set of first circuit means carried by the drum means, each of thefirst circuit means of the set being adapted to receive a data signalfrom a source without the drum means and apply the data signal to onedata gate of each set of data gates,

a clock gate carried by the drum means for each set of shift registermeans, each clock gate being connected to supply a clock pulse train toeach shift register means of a set when enabled,

second circuit means carried by the drum means for receiving a clockpulse train from a source without the drum means and applying the clockpulse train to each of the clock gates, and

synchronization circuit means carried by the drum means, thesynchronization circuit means being adapted to receive a synchronizationsignal related to the rotational position of the drum means from asource without the 'drum means and, in response to the synchronizationsignal, selectively enable the clock gate and the set of data gatesrelated to the respective matrices as the respective matrices travelthrough said predetermined portion of the revolution of the drum means.

References Cited UNITED STATES PATENTS 2,715,360 8/1955 Brown 101-922,930,347 3/1960 Metzger 178-23 15 2,951,121 8/1960 Conrad 178-3OXRICHARD B. WILKINSON, Primary Examiner.

JOSEPH W. HARTARY, Assistant Examiner.

